From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <ammarfaizi2@gnuweeb.org>
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org
X-Spam-Level: 
X-Spam-Status: No, score=-1.8 required=5.0 tests=ALL_TRUSTED,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,NO_DNS_FOR_FROM,
	URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6
Received: from [192.168.43.69] (unknown [182.2.38.152])
	by gnuweeb.org (Postfix) with ESMTPSA id 77DCC7E6C3;
	Mon,  7 Mar 2022 13:38:02 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gnuweeb.org;
	s=default; t=1646660289;
	bh=SPrR395Fio1xIoiYPHowYe9I1TFzu6lXoGUk7nXE7MI=;
	h=Date:To:Cc:References:From:Subject:In-Reply-To:From;
	b=Jq9W84JzC1kZQIJ+c+L2MvNXQuwzshExfw17fqYYar6573HmdZQIwmp6RV0AhVfwX
	 54XFyno3gpee1rt1KZ9eY1TaRM55VeOQ5s265kdMq0tdydfIOBiZa7VRLRU/NAsZc2
	 MbSJYBzAXJDCi2jQet8EN51Lxp+/MQbXdvzG7uWXeBf6MT37rdyp3sJ3/Db/N/t5TA
	 OQ94E5BY6ZjynVT5KnIu2713KsfsSwMSXJblJVNUnrAzfp/vOGS/RERxa49/n0+xZv
	 56B6k3oFheJ4RdjoXs4axKmvEDN8oLjO5jQhxsZEVLpFyy1C/FrXP0XVBh0znkSsLS
	 LVCiHEYgs+UQg==
Message-ID: <11dec988-0b4f-00f2-6fa6-8d08be95d106@gnuweeb.org>
Date: Mon, 7 Mar 2022 20:37:59 +0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Content-Language: en-US
To: Borislav Petkov <bp@alien8.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
 Dave Hansen <dave.hansen@linux.intel.com>, "H. Peter Anvin" <hpa@zytor.com>,
 Ingo Molnar <mingo@redhat.com>, Josh Poimboeuf <jpoimboe@redhat.com>,
 Juergen Gross <jgross@suse.com>, Kees Cook <keescook@chromium.org>,
 Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>,
 Tony Luck <tony.luck@intel.com>, Youquan Song <youquan.song@intel.com>,
 linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
 gwml@vger.gnuweeb.org, x86@kernel.org
References: <20220307114558.1234494-1-ammarfaizi2@gnuweeb.org>
 <YiX81kD/668UdFBr@nazgul.tnic>
From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Subject: Re: [PATCH v1 0/2] x86: Avoid using INC and DEC instructions on hot
 paths
In-Reply-To: <YiX81kD/668UdFBr@nazgul.tnic>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
List-Id: <gwml.vger.gnuweeb.org>

On 3/7/22 7:38 PM, Borislav Petkov wrote:
> On Mon, Mar 07, 2022 at 06:45:56PM +0700, Ammar Faizi wrote:
>> In order to take maximum advantage of out-of-order execution,
>> avoid using INC/DEC instructions when appropriate. INC/DEC only
>> writes to part of the flags register, which can cause a partial
>> flag register stall. This series replaces INC/DEC with ADD/SUB.
> 
> "Improvements" like that need to show in benchmark runs - not
> microbenchmark - that they bring anything. Just by looking at them, I'd
> say they won't show any difference. But I'm always open to surprises.

OK, thanks for taking a look. I will play a bit more with this. Not sure
how much the visible improvement. If I can win some numbers (probably can't),
I will be back to this thread.

> Btw, you don't have to send all your patches directly to me - there are
> other x86 maintainers. IOW, you can use scripts/get_maintainer.pl to
> figure out who to send them to.

I did anyway, all CC list here I took from that script. I will try to give
other maintainers a turn next time.

> Also, I'd advise going over Documentation/process/ if you're new to this.
> Especially Documentation/process/submitting-patches.rst.
I might've missed the benchmark backup part. Will review those documents again.

-- 
Ammar Faizi